One of the objectives of this project is to determine whether or not the mouse mammary tumor virus (MuMTV) requires association with genetic or carcinogenic factors to effect cell transformation. This will be approached by the experimental infection of permissive cells with MuMTV's produced in tissue culture. After exposure to sublethal doses of radiation or carcinogens, the infected cells will be monitored by the cell aggregation viability (CAV) assay for transformation and tested in vivo for tumorigenicity. A second objective is to assess the diagnostic value of antigens extracted from mouse mammary cell lines by the leucocyte migration inhibition assay (LMI). Comparative assays are to be done with antigens extracted from human breast tumor lines against peripheral leucocytes collected from normal and breast cancer patients.